And like grinding wheels

ABSTRACT

A peripheral grinding wheel wherein the peripheral grinding portion contains diamond or cubic boron nitride abrasive particles and is characterised in that it consists of two coaxial sections, the one section being a coarse section and containing coarse particles of between 60/80 mesh and 100/120 mesh and the other being a fine section containing fine particles of between 170/200 and 300/350 mesh, or in that it consists of a fine section sandwiched between two coarse sections, in each case the concentration of abrasive particle in the fine section preferably being greater than the concentration of abrasive particle in the coarse section.

United States Patent 1191 Lindenbeck 451 Apr. 9, 1974 [54] DIAMOND ANDLIKE GRINDING WHEELS 2,594,137 4/1952 Doermann 51/207 [75] Inventor:DirbAlmd Lindenbeck, Randburg, 1,616,53l 2/1927 Klllg 51/207 SouthAfrica 7 Primary Examiner-Donald G. Kelly [73] Assignee: EdenvaleEngineering Works Attorney, Agent, or Firm-v-Young & Thompson(Proprietary) Limited, zllliil'llnesblll'g, Transvaal, South ABSTRACT Aperipheral grinding wheel wherein the peripheral [21] Appl 248972grinding portion contains diamond or cubic boron nitride abrasiveparticles and is characterised in that it [30] Foreign ApplicationPriority Data consists of two co-axial sections, the one section beingMay 12, 1971 South Africa 71/3105 a coarse Section and Containing CoarsePattie!es f tween 60/80 mesh and 100/120 mesh and the other [52] US. Cl.51/207 being/a fine Section Containing fine Particles of 51 Int. Cl1124a 5/14 tween 170/200 n 300/550 in that it 531 Field f Search; 51 207204 20 1x20 4 sists of a fine section sandwiched between two coarse 5 29 R sections, in each case the concentration of abrasive 1 I particle inthe fine section preferably being greater 5 References Cited than theconcentration of abrasive particle in the UNITED STATES PATENTS3,067,55l 12/1962 Maginnis Si/207 X 7 Claims, 2 Drawing Figures DIAMONDAND LIKE GRINDING WHEELS Thisinvention relates to peripheral grindingwheels incorporating as abrasive particles diamond or cubic boronnitride. V f f f Peripheralgrinding wheels include a hub portion havinga central bore therein adapting the hub portion to be mounted on a shaftor spindle. The hub portion is itself formed from some suitable supportmaterial commonly used in the art such as steel, bakelite or a lightmetal. Carried on the periphery of the hubportion in a position to makeeffective contact with a workpiece, is the effective grinding portion.This portion commonly has a thickness of the, order of either onefourthinch or one-eighth inch (approximately 6 mm and 3 mm respectively). Thisperipheral portion has abrasive particles such as diamond embedded in acured synthetic resin or metal matrix.

Peripheral grinding wheels which incorporate abrasive particles such asaluminum oxide or silicon carbide can be suitably dressed both'forgoodgrinding efficiency, i.e. high stock removal, and for relatively lowgrinding efficiency, i.e. good surface finishing or polishing. When goodgrinding efficiency is first required then good polishing for a givenworkpiece, it is possible to dress the same wheel to achieve botheffects. However, dressing a peripheral grindingwheel incorporatingdiamond or cubic boron nitride is not easily achieved and hencedifferent wheels have in the past generally been required to achieveboth high stock remove] and good surfacefinish.

It is an object of the present invention to provide a peripheralgrinding wheelincorporating diamond or cubicboron nitride abrasiveparticles which minimises the abovementioned shortcomings of similarwheels of 5 the prior art. 1

According to the invention, there isprovided a peripheral grinding wheelhaving an'effective grinding portion containing diamond or cubic boronnitride abrasive particles, characterised in that the effective grindingportion, comprises two co-axial sections, the one section having coarseparticles and providing, in use, a high stock removal (hereinafterreferred to as the coarse section) and the other section having fineparticles and providing, in use, a good surface finish (hereinafterreferred to as the fine section");

In one form of the invention, the effective grinding portion consists oftwo such co-axial sections.

In another form of the invention, the effective grinding portionconsists of a central fine section sandwiched between two outer coarsesections.

The coarse section is preferably wider than the fine I section the widthin any given case being influenced by the amount of crossfeed duringgrinding. The widths of the sections will preferably be 20 percent ormore greater than the amount of crossfeed.

It has been found that particularly good results are achieved if theconcentration of abrasive particle in the fine section or sections isgreater than, preferably three times greater than, the concentration ofabrasive particle in the coarse section or sections. As is known,concentration is determined by taking the weight of abrasive particleper unit volume of the finished grinding element. The grinding elementin'this ease-is the effective grinding portion. The concentration isexpressed relative to a standard of where the weight of abra- Thepreferred concentrations of abrasive particle in the fine section willvary with matrix being used. In the case of a cured synthetic resinmatrix, the preferred concentration of abrasive particle in the finesection or sections is 100 to 150. In the case of a metal matrix, thepreferred concentration of the abrasive particle in the fi'ne'section orsections is 100 to 300.

The preferred concentration of abrasive particle in the coarse sectionorsections is 50 to 100, irrespective of the matrix material.

The fine abrasive particles preferably have a size between 170/2 00 meshand 300/350 mesh andthe size of the coarse particles is preferablybetween 60/80 mesh and 100/120 mesh.

To ensure good retention of the abrasive particles in the matrix of thewheel it is preferred that the particles are metal coated.

Two embodiments of the invention are described with reference to theaccompanying diagrammatic drawing which show, in end view, the effectivegrinding portions of two peripheral grinding wheels according to theinvention.

Referring now to FIG. 1, there is shown the effective grinding portion10 of a peripheral grinding wheel which consists of two co-axialsections 12 and 14. Section 12 is the fine section and contains finediamond grit of size 170/200 mesh while the section 14 is the coarsesection and contains coarse diamond grit of size 60/70 meshrThe gritconcentration of the fine section is (i.e. 108 carats per cubicinch).while the grit concentration of the coarse sectionis 50. Thematrix material for both sections is cured synthetic resin andthe-diamond grit is metal coated grit known as DX DA MC. e

In the wheel 20 of, FIG. 2, there are three sections, 22, 24 and26. Thesections 22 and 26 are the coarse sections with grit size andconcentration as for the section 14. The section 24 is the fine section,with grit size and concentration as for the section 12. The-matrixmaterial is again synthetic resin and the grit is DX DA MC.

In use, thewheels are used for grinding workpieces such as metalworkpieces. Considering first the wheel according to FIG. 2, 'a grindingprocess can be carried out with cross-feeds from opposite directions. Asthe grinding progresses, so the sharp edges 28 (shown in' dotted lines)of the effective grinding portion will be worn away and become rounded,as indicated in solid lines in the drawing. The outer sections 22, 26will remove-most of the material being ground whereas the centralsection 24 will polish the surface left by the outer sections.

Because of the curved profile of the wheel 20, a waviness may be left onthe workpiece surface. In order to reduce this waviness, the grindingwheel 10 of FIG. I may be used for grinding with the crossfeed beingapplied in only one direction i.e. the crossfeed of the workpiece in thedirection of the arrow 16. The profile of this wheel, in use, will haveless curvature than that shown in FIG. 2, the curvature being indicatedby solid lines in FIG. 1. This will have the effect of considerablyreducing the waviness. Furthermore, such a grinding process is moreefficient as a greater amount of the diamonds are used during grinding.Therefore, lower wheel costs and better surface finish are obtained whenan abrasive wheel, as shown in FIG. 1 is used with crossfeed in only onedirection.

The illustrated embodiments have been described using metal coateddiamond grit, but cubic boron nitride abrasive particles may also beused.

I claim:

1. A peripheral grinding wheel having an effective grinding portioncontaining abrasive particles selected from diamond and cubic boronnitride abrasive particles, characterised in that the effective grindingportion comprises two co-axial sections, the one section containingcoarse particles, from 60/80 mesh to 100/120 mesh in size, and the othersection containing fine particles, from 170/200 mesh to 300/350 mesh insize, and the concentration of abrasive particle in the sectioncontaining the fine particles being greater than the concentration ofabrasive particle in the section containing the coarse particles.

2. A wheel according to claim 1 wherein the effective grinding portionconsists of two and only two sections.

3. A wheel according to claim 1- wherein the efi'ective grinding portionconsists of a central section containing fine particles sandwichedbetween two outer sections containing coarse particles.

4. A wheel according to claim 1 wherein the ratio of the concentrationof abrasive particle in the section containing the fine particles to theconcentration of abrasive particle in the section containing the coarseparticles is 3:1.

5. A wheel according to claim 1 wherein the matrix of the effectivegrinding portion is a cured synthetic resin and the concentration of theabrasive particle in the section containing the fine particles is to andthe concentration of the abrasive particle in the section containing thecoarse particles is 50 to 100.

6. A wheel according to claim 1 wherein the matrix of the effectivegrinding portion is a matrix metal and the concentration of abrasiveparticle in the section containing the fine particles is 100 to 300 andthe concentration of abrasive particle in the section containing thecoarse particles is 50 to 100.

7. A wheel according to claim 1 wherein the abrasiv particles are metalcoated.

1. A peripheral grinding wheel having an effective grinding portioncontaining abrasive particles selected from diamond and cubic boronnitride abrasive particles, characterised in that the effective grindingportion comprises two co-axial sections, the one section containingcoarse particles, from 60/80 mesh to 100/120 mesh in size, and the othersection containing fine particles, from 170/200 mesh to 300/350 mesh insize, and the concentration of abrasive particle in the sectioncontaining the fine particles being greater than the concentration ofabrasive particle in the section containing the coarse particles.
 2. Awheel according to claim 1 wherein the effective grinding portionconsists of two and only two sections.
 3. A wheel according to claim 1wherein the effective grinding portion consists of a central sectioncontaining fine particles sandwiched between two outer sectionscontaining coarse particles.
 4. A wheel according to claim 1 wherein theratio of the concentration of abrasive particle in the sectioncontaining the fine particles to the concentration of abrasive particlein the section containing the coarse particles is 3:1.
 5. A wheelaccording to claim 1 wherein the matrix of the effective grindingportion is a cured synthetic resin and the concentration of the abrasiveparticle in the section containing the fine particles is 100 to 150 andthe concentration of the abrasive particle in the section containing thecoarse particles is 50 to
 100. 6. A wheel according to claim 1 whereinthe matrix of the effective grinding portion is a matrix metal and theconcentration of abrasive particle in the section containing the fineparticles is 100 to 300 and the concentration of abrasive particle inthe section containing the coarse particles is 50 to
 100. 7. A wheelaccording to claim 1 wherein the abrasive particles are metal coated.